Remove call to deprecated is_gray function
Misc doc string fixes
Only clip for ndimage.map_coordinates case
Add note about internal usage of transformation matrix
Add support for matrix as inverse_map
Improve example of warp function to show all available options
Fix deprecated function name in example
Merge pull request #750 from ahojnnes/misc

Misc cleanups.
PEP8: comparison
MAINT: unused import
MAINT: matplotlib is in requierements.txt
DOC: no import numpy in doc
DOC: add missing import
PEP8: fix indentation
PEP8